The present invention relates to improvements in metal halogen battery systems, and more particularly the invention relates to an improved metal halogen battery construction which includes an effective hydrogen/halogen reactor which can operate safely and efficiently at virtually all hydrogen/halogen concentrations within the temperature limits of present container materials.
The electrical energy storage systems of the type referred to herein (e.g., a zinc-chlorine battery system) utilizes a halogen hydrate as the source of a halogen component for reduction at a normally positive electrode, and an oxidizable metal adapted to become oxidized at a normally negative electrode during the normal discharge of the storage system. An aqueous electrolyte is employed for replenishing the supply of the halogen component as it becomes reduced at the positive electrode. The electrolyte contains the dissolved ions of the oxidized metal and the reduced halogen and is circulated between the electrode area and a storage area containing halogen hydrate which progressively decomposes during a normal discharge of the electrical energy system, liberating additional elemental halogen to be consumed at the positive electrode. Electrical energy storage systems or battery systems of this type are described in prior patents owned by the same assignee as the present invention such as U.S. Pat. Nos. 3,713,888, 3,993,502, 4,001,036, and 4,146,680. Such systems are also described in published reports prepared by the assignee herein, such as EPRI Report EM-1051 (Parts 1-3) dated April 1979, published by the Electric Power Research Institute. The specific teachings of the aforementioned U.S. patents and the EPRI Report are incorporated herein by reference.
During the cycling of a metal halogen battery, such as for example a zinc-chlorine battery, small amounts of hydrogen are generated at the zinc electrode. The hydrogen gas is normally recombined with chlorine gas to form hydrogen chloride by means of a chemical reaction (see page 15-11 of EPRI Report EM-1051). At low hydrogen concentrations (e.g., about 1-5%) the reaction proceeds smoothly. However, under certain conditions hydrogen gas may accumulate in the battery system and this can be troublesome, because at higher hydrogen concentrations (e.g., about 10% or greater), the reaction between hydrogen and chlorine becomes self propagating, and thus there may be generated pressure fronts capable of breaking or rupturing the battery container. Moreover previous techniques for carrying out the reaction (such as shown at page 15-11 of EPRI Report EM-1051) are not satisfactory at higher hydrogen concentrations or buildups. This is a significant problem, particularly with respect to the usage of such battery systems in mobile applications.
Under a variety of operating conditions, it is in many instances desirable to allow the hydrogen concentrations to build up to significant levels within the battery system. Eventually, however, to maintain the pH of the system, the hydrogen must be recombined with chlorine to reform hydrogen chloride in a safe and reliable manner. In certain instances, with high concentrations of hydrogen, in order to prevent propagation of a flame front back into the battery gas space, a flame arrester has been inserted between the reactor and the gas space. This type of technique is discussed in commonly assigned co-pending U.S. application Ser. No. 316,044 filed Oct. 28, 1981 by Hammond et al. Their combustion arrester technique works satisfactorily, however, at particularly high hydrogen concentrations, the reaction temperature in the gas space may well exceed the temperatures at which the reaction container materials are stable. In the present invention an effective hydrogen/halogen reactor is disclosed that can operate safely and efficiently at all hydrogen/halogen concentrations within the temperature limits of present container materials.